1. Field of the Invention
The present disclosure relates generally to an image forming apparatus, and, more particularly, to an image forming apparatus equipped with a fusing unit to fuse developing agent onto a print medium and a method of controlling the same.
2. Description of the Related Art
In general, an image forming apparatus forms an image on a print medium according to input image signals, and may include, for example, a printer, a copy machine, a facsimile and a multi-functional peripheral (MFP) having a combination of several functions of the above devices.
An image forming apparatus typically include a body or casing accommodating therein several components, such as, for example, a print medium supplying unit, a developing unit, an exposing unit, a fusing unit and a print medium discharging unit. The body may form the external appearance of the image forming apparatus. The print medium supplying unit stores a plurality of print media on which the images are to be formed. The developing unit applies developing agent to an electrostatic latent image to develop the same into a visible image. The electrostatic latent image may be formed by irradiating light onto a photosensitive member that had been pre-charged. The photosensitive member may be provided as a part of the developing unit, for example, which applies developing agent, e.g., toner, on the electrostatic latent image to develop the electrostatic latent image into the visible image. Subsequently, the visible image developed on the photosensitive member is transferred to a print medium supplied from the print medium supplying unit. After the visible developer image is transferred to a print medium, the fusing unit is utilized to fuse or fix the developing agent on the print medium. The print medium discharging unit discharges the print medium bearing the fixed developer image out of the body of the image forming apparatus.
A known fusing unit may be of a configuration that includes a pressing roller, a heating belt, a pair of support rollers and a heater. In such configuration, the heating belt may be arranged to move in close contact with an outer surface of the pressing roller. The support rollers may be arranged to support the inner portions of the heating belt. The heater may provide the heat to the heating belt. In the above described configuration, when the print medium, on which the developing agent has been transferred, passes through between the pressing roller and the heating belt, heat and pressure are applied to the print medium so that the developing agent is fused onto the print medium.
During the fusing process, however, an amount of charge in the developing agent may become reduced, resulting in a lowered adhesion of the developing agent to the print medium. For example, as moisture evaporates from the print medium due to the heat applied from the heating belt, some of the developing agent may even become detached from the print medium, resulting in a so-called “line burst phenomenon.”
Known attempts to reduce the occurrences of the line burst phenomenon include supplying the pressing roller with an electrical potential of a polarity opposite to that of the developing agent so as to cause the print medium to have a polarity opposite to that of the developing agent, resulting in an electrical attractive force acting between the developing agent and the print medium. For example, when the developing agent is charged with a negative polarity, a positive voltage is applied to the pressing roller so that the print medium is charged with a positive polarity. The electrical attractive force between the oppositely charged print medium and developing agent may help to reduce the line burst phenomenon.
However, unfortunately, while helpful in some respect as above described, when the heating belt is brought into contact with the pressing roller exhibiting a polarity, for example, a positive polarity, the surface of the heating belt may also gradually become charged with the positive polarity by the pressing roller. Such heating belt charged with a polarity may attract the developing agent charged with an opposite polarity, such attraction of which may result in a lower fusing efficiency.